An eye diagram is a methodology to represent and analyze high speed digital signals (such as optical and base band signals), their quality and the ability to perform clock and data recovery.
Some high-speed digital standards use a form of non-return to zero (NRZ) for the data coding where a high (positive) pulse represents a logic one and a low (negative) pulse a logic zero. Other standards use more complex waveforms (i.e., modulation schemes), such as PAM-4 or PAM-8. For all waveforms, the eye diagram allows parameters of the electrical quality of the signal to be visualized. The data eye diagram is constructed from a digital waveform by folding the parts of the waveform corresponding to each individual symbol into a single graph with signal amplitude on the vertical axis and time on horizontal axis. This construction is repeated over many samples of the waveform, the resultant graph will represent the average statistics of the signal and will resemble an eye. The eye opening corresponds to one symbol period and is typically called the Unit Interval (UI) width of the eye diagram. The eye diagram offers additional information beyond the time domain waveform display, including impairments such as attenuation, noise, crosstalk, etc. Eye Diagrams are typically used to characterize a high speed signal source or transmitter (receiver testing usually requires bit error rate testing).
Conventional techniques for generating an eye diagram of a digital signal require using testing instruments that receive a repetitive trigger from a clock, sample and plot the signal again and again on a display screen. Other techniques sample the signal in several phases, in order to complete the diagram. However, these techniques need a lot of information to capture the eye diagram (histogram per all the phases) and some may take a relatively long time to create.
It is therefore an object of the present invention to provide a system and method for estimating an eye diagram of a signal that passes a communication channel, based on signal statistics collection.
It is another object of the present invention to provide a system and method for estimating an eye diagram of a signal which do not need to store all the information of all the phases.
It is a further object of the present invention to provide a system and method for estimating an eye diagram of a signal that passes a communication channel, which does not require collection of data for long time periods.
Other objects and advantages of the invention will become apparent as the description proceeds.